A cursory look at election results in very white areas across the deep south and Appalachia TN, AL and West Virginia has me wondering. Obama was getting 25 to 30 percent ( 30 percent in rural white Jackson County Alabama) on average in 2008. In 2020, Biden was averaging teens and low 20s. How was an African American pulling in slightly more in white Deep South areas than Biden a white person?
Ancestral Democrats as trend never happens at once. Also environmental policy pushed even more away. If someone is a life long Democrat but feels party drifting away, often takes a few election cycles before finally switch. Likewise Trump's more brash style probably helped as McCain and Romney had less appeal in this area than Trump.
In addition could be demographic churn as Appalachia was helped a lot by FDR since in 2008 the last of those who remember New Deal era would still be alive, but by 2020 mostly dead and many of those were life long Democrats but children, grandchildren, and great grand children were not.